Page 481 - Handbook of Adhesives and Sealants

Selection of Adhesives 417

of these decisions cannot be made independently. The substrate selec-
tion, for example, may influence the processing conditions and joint
design that is necessary. Therefore, the adhesive selection must be
made considering all of the parameters involved in the bonding pro-
cess.
What should be considered first? If you choose an adhesive based
on the maximum adhesion to the substrates selected, you may be se-
verely limiting yourself with respect to curing processes or environ-
mental resistance. Likewise, if you select an adhesive based only on
its resistance to service conditions, you may have to redesign the joint
and find that the selected substrates are now not possible (or cost
effective) to manufacture in the required configuration. This provides
the individual selecting the adhesive system with a formidable prob-
lem. What characteristics are most important and how should one go
through the process of selecting an appropriate adhesive?
To achieve optimum results, every stage of the bonding process must
be well planned and thought out. After this analysis, if the estimates
of strength, durability, and cost do not appear to provide an adequate
safety margin, then one must go back through the entire process, mak-
ing refinements where they can be made to end with a truly optimized
result. The following approach is often recommended when using en-
gineering adhesives. 1
1. Consider alternative assembly and bonding processes. There are
several joining processes available to the design engineer. These need
to be considered before time and resources are committed to any sin-
gular joining method.
2. Gather all information possible regarding the resulting product
and its requirements. This will include identification of possible alter-
native substrates, joint designs, and available processing facilities. De-
termine the environmental conditions and types of loading that the
joint must resist. Plan all phases of the joining process, from selecting
the substrates to deciding on quality control methods.
3. Design the joint especially for the method of bonding that is cho-
sen. Consider the service conditions and stresses that the joint is ex-
pected to encounter in service.
4. Choose the appropriate adhesive in cooperation with an adhesive
supplier. Estimate the required adhesive strength and durability.
5. Ensure the reliability of the adhesive bond by engaging in a test-
ing program to verify the durability of the joint by simulating actual
assembly practices and aging environments. This testing program
should also determine the optimum bond dimensions and thickness.
Steps 1 and 2 are considered planning processes and they are de-
scribed below. Steps 3 through 5 are production decisions that utilize